1. Field of the Invention
The present invention relates to an image processing apparatus having compression/expansion function for image data and display function therefor, and more particularly to an image processing apparatus utilizing the JBIG method.
2. Related Background Art
In the conventional word processor or the like equipped with the window display system, there has been observed difference in resolution, between the image data obtained by a scanner and the display data for a CRT.
For example when the image obtained by an image scanner has a resolution of 400 dpi while the CRT has a resolution of 100 dpi, there has been conducted a conversion from 400 to 100 dpi, in order to obtain image data for display.
Similarly, in the display image buffer, there have been stored image data of 100 dpi.
Also it has been very difficult to display the image in the high-speed page flipping mode in which the image frames are scrolled at a high speed, in the unit of a page. In such high-speed page flipping mode, because of the limitation in the speed or in the memory capacity, the images are not displayed but the page number alone is varied with the blank image frame. For example, in case of image display with the image data compressed by the conventional MMR compression/expansion method, image data which are compressed from the image of 400 dpi by said MMR method and stored in a rigid disk or a floppy disk, are converted into the image data of 400 dpi by an expansion circuit and stored in an image memory. Then said image data of 400 dpi are read from-the image memory and compressed to 100 dpi by a compression circuit, then are transferred and stored in a VRAM, and are displayed on a display device such as CRT. Since such expansion and compression require time, it has been difficult to execute the high-speed page flipping with image display, or so-called high-speed image display.
Naturally such high-speed page flipping with image display is theoretically possible by effecting such page flipping operation after all the image data of 100 dpi to be subjected to the high-speed page flipping are stored in the VRAM or the like, such operation is practically unacceptable, because a long time is required for preparation and a large memory capacity is required in the VRAM. Also in a system which does not employ compressed data, the image memory is generally designed for 400 dpi which is the resolution of the scanner or the printer, and the image display is executed by compressing the data to the resolution of CRT of 100 dpi and transferring thus compressed data to the VRAM for display. Consequently, in consideration of the speed .and the required memory capacity, the high-speed page flipping operation, involving a large amount of images, has been conducted without the image display.
The clipping operation, for clipping a partial image displayed on the display frame for making an icon, requires several seconds to about twenty seconds for each image because it involves image compression for preparing a reduced image. In the conventional process, after the user designates the clipping area of the image, said image remains displayed in its original size during the clipping operation in the apparatus, and said image suddenly vanishes when the clipping operation is completed.
In the general image display on a display device such as CRT, the display image data are stored in the unit of a page in a display image buffer area in the main memory, then said data are transferred to the VRAM, and the images are displayed in succession, in the unit of a page at a time, on the display device such as CRT through said VRAM. Consequently, when the capacity of the residual memory area of the display image buffer area becomes less than an image frame, the storage of the display image data is interrupted at this point and the subsequent images cannot be displayed.
In case the icons for an image file are not prepared by the application software, such icons have to be prepared by the operator. However, since it is difficult to display all the necessary information in the icons, it has generally been conducted to display a text of a certain number of characters in the icon, or to display icons fixed in advance in the system.
However, the conventional technology explained above has been associated with the following drawbacks:
(1) The image data for display have to be obtained by conversion from the real image data;
(2) Such conversion is indispensable even for merely obtaining the image data for display;
(3) The capacity of the image memory may become deficient in case of storing a large number of display image data;
(4) The conventional high-speed page flipping operation has been very inconvenient for the selection or retrieval of images, since, in such operation, the images are not displayed but the page number alone is varied;
(5) In the clipping operation of image data, the image to be clipped remains displayed in the course of said operation, and said image suddenly vanishes thereafter. Thus the user feels uneasy and inconvenient, as the progress of the operation is unclear to the user;
(6) When the capacity of the residual memory area of the display image buffer area becomes less than an image frame, the image display is automatically interrupted even if a considerable residual area still exists. Such mode of operation is inconvenient to the user, and is undesirable for the effective utilization of the memory; and
(7) The number of icons often increases for an image file, and the image represented by the icon sometimes becomes forgotten and uncomprehendable after a time.